Exploring the application of TEX86 and the sources of organic matter in the Antarctic coastal region

Isoprenoidal glycerol dialkyl glycerol tetraethers (isoGDGTs) are archaeal biomarkers. In many settings, the degree of cyclization of isoGDGTs is correlated with temperature, forming the basis of the TEX86 paleothermometer that is widely used to reconstruct sea surface temperature (SST) across a range of time scales. However, the application of TEX86 to the polar regions is relatively limited and there is currently no consensus on which calibration is best suited for polar environments. In addition, application of TEX86 to the polar regions is complicated by uncertainty regarding the source of organic matter input in coastal polar environments. We tested five different calibrations for TEX86 in marine sediments from the Antarctic coastal region of Admiralty Bay near King George Island, using four short cores that span the second half of the 20th century. We also explored the possible sources of organic matter in these cores using sterol biomarkers. Best results for TEX86 were obtained using a quadratic calibration. The TEX86 signal presented a strong seasonal signal and best matched reanalysis temperatures of the austral spring season (Oct-Nov-Dec). The most abundant compounds observed in the sediments were the sterols cholest-5-en-3 beta-ol and 24-ethylcholest-5-en-3 beta-ol, the fatty alcohols C16 and phytol, and isoGDGT-0, indicating a dominant marine origin of the organic matter. Differences in their vertical distributions suggests that some compounds (such as cholest-5-en-3 beta-ol and phytol) may have had different sources over the evaluated period. Together our results indicate that TEX86 can be used to reconstruct SSTs in the Antarctic coastal region.

Automated summary

IsoGDGTs are archaeal biomarkers that can be used to reconstruct sea surface temperatures. The TEX86 paleothermometer is widely utilized for this purpose, however its application to polar regions remains limited. This study tested different calibrations for TEX86 in Antarctic coastal sediments and found that a quadratic calibration yielded the best results, indicating the potential for using TEX86 to reconstruct SSTs in the Antarctic coastal region. Sterol biomarkers suggested a dominant marine source of organic matter in the sediments, with seasonal variations in TEX86 signal and differences in compound sources over time.